JP6433740B2 - Gold nanoparticle-containing carbon thin film electrode for electrochemical measurement and arsenic ion electrochemical detection method using the electrode - Google Patents

Description

  The present invention is a gold nanoparticle-containing carbon thin film electrode and an arsenic ion electrochemical detection method using the electrode, and more specifically, water quality, soil environment, work environment, food / geological / biological poisoning, etc. The present invention relates to a carbon thin film electrode suitable for use in electrochemical analysis or an electrochemical sensor and an electrochemical detection method for arsenic ions using the same.

Arsenic (As) is an element that is easily taken into the human body by ingestion from food and drinking water, etc. Even if it is a trace amount, it accumulates in the human body, causing arsenic poisoning, and in the worst case, extremely dangerous leading to death Element.
The sources of arsenic (metal arsenic and arsenic compounds) into the environment are naturally occurring sources and anthropogenic sources. Natural sources can be natural during rolling of soil particles, volcanic activity, seawater and plant development. It occurs in the atmosphere and is released into the atmosphere. Arsenic, when combined with gallium, indium, and aluminum, turns into a high-performance semiconductor that cannot be realized with other metals, and is therefore used industrially as a light-emitting diode, semiconductor laser, or optical communication material. Therefore, arsenic is toxic but is an indispensable element for industry, and it can be considered that such industrial waste is discharged into the atmosphere and water. When the arsenic compound is dissolved in ground water and taken into the human body as drinking water, the above-described arsenic poisoning may occur.

The standard for arsenic emission in the Water Pollution Control Act is regulated to 100 ppb or less, and the standard for arsenic in drinking water by WHO, EPA, and the Ministry of the Environment is regulated to 10 ppb or less. Therefore, it is required to detect arsenic and arsenic compounds of factory wastewater and drinking water simply and with high sensitivity.
EPA's official methods include inductively coupled plasma-mass spectrometry (ICP-MS) (Method 200.8), inductively coupled plasma-atomic emission spectrometry (ICP-AES) (Method 200.7), graphite furnace atomic adsorption spectrometry (Method 200.9) and the like, and each detection lower limit is 1.4, 8, 0.5 ppb (Non-patent Document 1), which is a very sensitive measurement method. On the other hand, since the apparatus is expensive and the pretreatment time is long, problems remain in terms of simple and highly sensitive measurement.
EPA also recommends the anodic stripping voltammetry (ASV) method, which is an electrochemical method, for arsenic analysis (Method 7063) (Non-patent Document 2). The ASV method is an analytical method that detects the oxidation current value obtained by reducing and depositing metal ions once on the electrode and oxidizing the deposited metal. This is an analysis method suitable for on-site analysis.

As working electrodes used for arsenic measurement using the ASV method, mercury, platinum, gold (Au), etc. have been reported for a long time, and their performance is known to be greatly influenced by the electrode materials used. Yes. Among these noble metal electrode materials, the Au electrode has no toxicity like mercury and forms an intermetallic bond between arsenic during the reduction reaction, and this intermetallic compound of Au-As can be easily detected by the oxidation reaction in the ASV measurement. It has been reported (Non-patent document 3, Patent document 1). Furthermore, it has been reported that Au (Non-Patent Document 4) or Au nanoparticles (Non-Patent Document 5) can be dispersed on a carbon electrode to improve the lower limit of detection of arsenic than an Au single electrode. However, As analysis using electrodes coated with Au on carbon rich in sp ² carbon bonds, such as graphite electrodes and GC electrodes, it is difficult to obtain a stable signal, and the accuracy and stability are low. It has been reported (Non-Patent Document 4).

Further, arsenic measurement using an electrode in which a boron-doped diamond (BDD) electrode is modified with gold has been studied (Patent Document 2, Non-Patent Document 6). In contrast to the carbon electrode described above, the BDD electrode is composed of sp ³ bonding components in the carbon, so a stable and lower background current can be realized than the commonly used carbon electrode. It has the advantages such as. However, although BDD is a stable electrode, the electrodeposition efficiency of Au is poor, and the lower limit of As detection for the BDD electrode electrodeposited with Au was 2.85 ppb (Non-patent Document 6). It has also been reported that by simultaneously depositing Au and As in order to increase the electrodeposition efficiency, As can be measured stably and with high sensitivity (Non-patent Document 7 and Patent Document 3). However, the above-mentioned gold electrodeposited carbon electrode still has a problem that requires a step of electrodepositing the electrode. Furthermore, when the BDD electrode electrodeposited with Au is used repeatedly, gold adhering to the surface may be eluted, which further causes a problem that sensitivity is further lowered and reproducibility is difficult to obtain (Patent Document 2).

JP 2007-304081 A JP 2008-216061 A JP 2010-271236 A JP 2006-90875 A JP 2003-121407 A

EPA Report, EPA-815-R-00-010, December (1999) Pyle et al, US EPA (1996) Prakash et al., Electroanalysis 15, 1410 (2003) Viltchinskaia et al., Electroanalysis 9, 633 (1997) Dai et al., Anal. Chem. 76, 5924 (2004) Simm et al., Analyst 130, 1303 (2005) McGaw et al., Anal. Chim. Acta 575, 180 (2006)

  From the background as described above, the present invention provides a gold nanoparticle-containing carbon thin film electrode having sufficient conductivity as an electrode and having an excellent electrocatalytic activity for arsenic, and a simple production method thereof. It is an object to do.

  The inventors have invented a new conductive carbon electrode (Patent Document 4) and a metal nanoparticle-containing carbon electrode (Patent Document 5). In the conventional method for producing metal nanoparticle-containing carbon electrodes by sputtering, carbon and metal are sputtered on a substrate by placing a metal target together on the carbon target and applying a voltage to the carbon target. (See FIG. 1b). However, in the conventional sputtering method using a metal target arranged in a carbon target, the same voltage is applied to the carbon component and the metal component in the target, so that a metal having a high sputtering speed precedes the carbon. Thus, there is a problem that it is difficult to precisely control the content of metal nanoparticles in the formed thin film. In particular, when trying to increase the content of metal particles in the electrode, it is necessary to increase the surface area of the metal target disposed together on the carbon target. The use makes it possible to contain a metal component corresponding to the surface area ratio in the electrode, while the introduction as metal nanoparticles in the electrode is unevenly distributed, and an electrode that can withstand practical use is manufactured. I couldn't.

The inventors of the present invention have intensively studied in view of such problems, and when producing a carbon thin film electrode by a sputtering method represented by unbalanced magnetron (UBM) sputtering, a carbon target and gold (Au). When the target power with the target is sputtered simultaneously in a controllable state, a carbon thin film electrode in which gold nanoparticles are uniformly dispersed in a carbon thin film electrode having a microcrystalline domain in which sp ² bonds and sp ³ bonds are mixed is formed. It was found that it can be obtained. Further, the obtained gold nanoparticle-containing carbon thin film electrode has good electrocatalytic activity for electrochemical detection of arsenic, and has found that measurement stability and storage stability are greatly improved. The present invention has been completed.

That is, the present invention
A carbon thin film electrode for electrochemical measurement for detecting arsenic ions in a solution to be measured by electrode reaction based on reduction deposition and oxidation elution,
The carbon thin film electrode for electrochemical measurement is composed of a microcrystalline domain in which sp ² bonds and sp ³ bonds are mixed with respect to the bonding mode between carbons, and thereby has a wider range of potential than graphite carbon and glassy carbon electrodes. The present invention relates to a carbon thin film electrode for electrochemical measurement characterized by having a window and containing gold nanoparticles uniformly.

Here, in one embodiment of the carbon thin film electrode for electrochemical measurement of the present invention, the content of the gold nanoparticles is 10 to 22 at%.
In one embodiment of the carbon thin film electrode for electrochemical measurement of the present invention, the carbon thin film electrode is formed on the substrate by independently controlling the sputtering power of the carbon target and the gold target in the sputtering method. It is characterized by comprising a carbon thin film formed.
Further, in one embodiment of the carbon thin film electrode for electrochemical measurements of the present invention, the sum of the number of sp ² bonded atoms and the number of sp ³ bonded atoms between carbons constituting the carbon thin film electrode. The atomic ratio of the number of sp ³ bonded atoms to is in the range of 0.1 to 0.4.
In one embodiment of the carbon thin film electrode for electrochemical measurements of the present invention, the gold nanoparticles have a particle size of 7 nm or less.
In addition, the carbon thin film electrode for electrochemical measurement of the present invention includes a combination of two or more of the features described above as an embodiment of the carbon thin film electrode for electrochemical measurement of the present invention.

According to another aspect of the present invention, the present invention provides:
An electrochemical measurement method for detecting a concentration of arsenic ions in a measurement target solution by a reaction based on reduction deposition and oxidation elution using a counter electrode and a working electrode composed of the carbon thin film electrode for electrochemical measurement,
A reduction deposition step of reducing and depositing arsenic on the surface of the working electrode made of the carbon thin film electrode by changing the potential of the working electrode made of the carbon thin film electrode in a negative potential direction, and a positive potential of the working electrode made of the carbon thin film electrode The present invention relates to an electrochemical measurement method for arsenic ions, comprising an oxidation elution step of eluting arsenic electrodeposited on the surface of the carbon thin film electrode into the measurement target solution by sweeping in a potential direction.

According to another aspect of the present invention,
An apparatus for electrochemically measuring the concentration of arsenic ions in a solution to be measured,
A cell containing a counter electrode and a working electrode composed of the carbon thin film electrode for electrochemical measurement;
A potential for reducing and depositing arsenic on the surface of the working electrode made of the carbon thin film electrode is supplied by changing a potential of the working electrode made of the carbon thin film electrode in a negative potential direction, and then the working electrode made of the carbon thin film electrode And a potential changing means for supplying a potential for eluting arsenic deposited on the working electrode made of the carbon thin film electrode into the measurement object solution;
The present invention relates to an electrochemical measurement apparatus for measuring the concentration of arsenic ions, comprising a detection means for detecting a current change accompanying a change in potential of a working electrode made of the carbon thin film electrode.

According to another aspect of the present invention,
A method for producing a gold thin film-containing carbon thin film electrode for detecting arsenic ions in a solution to be measured by an electrochemical measurement method,
The method includes forming a gold nanoparticle-containing carbon thin film electrode on a substrate by sputtering, and forming a film while independently controlling the target power of the carbon target and the gold target.
Thus, the present invention relates to a production method characterized in that the gold nanoparticle content in the gold nanoparticle-containing carbon thin film electrode is controlled.

  According to the present invention, a carbon thin film electrode containing gold nanoparticles superior in arsenic electrochemical measurement can be easily produced without going through a gold electrodeposition step. Since the gold nanoparticle-containing carbon thin film electrode is formed by independently controlling the gold component and the carbon component, the content of the gold nanoparticle can be controlled with good reproducibility. Thereby, the gold component contained in the carbon thin film electrode can be uniformly distributed in the form of gold nanoparticles in the electrode. The obtained gold nanoparticle-containing carbon thin film electrode has a structure in which at least a part of the gold nanoparticle, which is an electrocatalytic active portion, is embedded in the form exposed on the surface of the electrode. In addition, there is almost no possibility that gold nanoparticles will be eluted and dropped off during long-term storage. Therefore, it is possible to provide a carbon thin film electrode capable of measuring arsenic with higher sensitivity and stability than conventional gold electrodeposited carbon thin film electrodes and the like.

FIG. 1 (a) is a schematic view showing the relationship between the arrangement of a substrate, a carbon target, and a metal target in a sputtering apparatus capable of producing a gold nanoparticle-containing carbon thin film electrode of the present invention. FIG.1 (b) is the schematic which shows the relationship of the arrangement | positioning of a board | substrate, a carbon target, and a metal target in the conventional sputtering device for producing the metal nanoparticle containing carbon thin film electrode. FIG. 2 shows an image when the gold nanoparticle-containing carbon thin film electrode produced in Example 2 below was observed using a transmission electron microscope. FIG. 3A shows square wave voltammograms when trivalent arsenic ions at various concentrations were measured using a gold nanoparticle-containing carbon thin film electrode as a working electrode in Example 3 below. FIG. 3B is a graph showing the relationship between the peak current density obtained from the voltammogram of FIG. 3A and the trivalent arsenic ion concentration. In the following Example 4, it is a graph which shows the measurement stability at the time of measuring trivalent arsenic ion of 100 ppb, using a gold nanoparticle containing carbon thin film electrode as a working electrode. In FIG. 4, the solid line indicates the initial measurement result, and the dotted line indicates the measurement result with the electrode that was dried for 24 hours in the atmosphere at room temperature after the electrode surface was dried with nitrogen gas. In the following comparative example, it is a graph which shows the measurement stability at the time of measuring a trivalent arsenic ion of 100 ppb, using a gold electrodeposition glassy carbon (GC) thin film as a working electrode. In FIG. 5, the solid line shows the initial measurement result, and the dotted line shows the measurement result with the electrode that was dried for 24 hours at room temperature in the atmosphere after the electrode surface was dried with nitrogen gas.

The gold nanoparticle-containing carbon thin film electrode for electrochemical measurement according to the present invention detects arsenic ions in a solution to be measured by electrode reaction based on reduction deposition and oxidation elution. The gold nanoparticle-containing carbon thin film electrode of the present invention is composed of microcrystalline domains having carbon-carbon bonds in which sp ² bonds (graphite structure) and sp ³ bonds (diamond structure) are mixed. Features. That is, the microcrystalline domain (graphite structure) composed of sp ² bonds is composed of microcrystalline domains connected by sp ³ bonds. The size (major axis) of each microcrystalline domain is usually about 0.5 nm to 100 nm. The size of the microcrystalline domain can be controlled by adjusting the acceleration voltage of irradiated ions.

Such a carbon thin film electrode composed of a microcrystalline domain in which sp ² bonds and sp ³ bonds are mixed has high conductivity, and an electrochemically irreversible measurement target substance is reacted on the electrode. It is characterized by substantially not adsorbing film on the electrode even after. This carbon thin film electrode for electrochemical measurements has a stable and wide potential window compared to conventional glassy carbon electrodes and graphite electrodes by including microcrystalline domains containing many sp ³ bonds like diamond electrodes. It is characterized by. In addition, by including sp ² bonds, the conductivity is lower than that of graphite, but the conductivity is sufficient for electrochemical measurement, and it is not necessary to perform doping as in a diamond thin film.

In microcrystalline domains that constitute the gold nanoparticle-containing carbon film electrode of the present invention, the carbon to the sum of the number of carbon atom and sp ² bonded carbon atoms that are sp ³ bonds, and sp ³ bonds The atomic ratio of the number of atoms (sp ³ bond atom number / sp ² bond atom number + sp ³ bond atom number) is within a range having the characteristics obtained by mixing the above-described sp ² bond and sp ³ bond. Although not particularly limited, it is preferably in the range of 0.1 to 0.4. When the atomic ratio is in the range of 0.1 to 0.4, the potential window is significantly wider than that of the graphite carbon electrode or the glassy carbon electrode, and a measurement object having a high oxidation potential can be detected as a clearer current signal. In this case, the potential window can be widened by about ± 200 mV or more in the positive direction and the negative direction, respectively, as compared with the conventional graphite carbon electrode or glassy carbon electrode.

Note that the ratio of the above-described atomic ratio between sp ² bonds and sp ³ bonds between carbons can be appropriately controlled by adjusting the acceleration voltage of irradiation ions irradiated during film formation. The ion acceleration voltage can be controlled by applying an RF or DC bias to the substrate and adjusting the bias voltage. When the ion pressurization voltage was changed from 20V to 150V, the ratio of sp ³ bonds was the highest at 150V. Accordingly, those skilled in the art can appropriately adjust the acceleration voltage of the irradiated ions so that the above-described preferable atomic ratio is obtained.

The above atomic ratio regarding sp ² bond and sp ³ bond can be measured by X-ray photoelectron spectroscopy (XPS). That is, the binding energy (eV) and strength (CPS) are measured by XPS, and the binding energy (eV) is plotted on the horizontal axis and the strength (CPS) is plotted on the vertical axis. The curve representing the sp ³ bond has a peak at 285.3 eV, and the curve representing the sp ² bond has a peak at 284.3 eV. By taking the ratio of these peak heights, the sp ³ bond / sp ² bond can be calculated. From this, the above atomic ratio (number of sp ³ bond / number of sp ² bond + number of sp ³ bond) ) Can be calculated.

Moreover, the carbon thin film electrode for electrochemical measurements of the present invention is characterized by containing gold nanoparticles uniformly in the electrode. In addition, in the conventional method for producing metal nanoparticle-containing carbon electrodes by sputtering, the metal having a high sputter rate is sputtered prior to the carbon, so that the amount of introduced metal nanoparticles in the electrode is controlled and distributed. Had a problem that caused bias. However, according to the carbon thin film electrode of the present invention, by independently controlling the sputtering of the carbon component and the gold component, the gold component is uniformly distributed in the carbon thin film electrode at a desired concentration and in the form of nanoparticles. It became possible. Thus, an electrode in which gold nanoparticles are uniformly distributed is preferable in terms of realizing a stable embedded structure and high electrode activity.
In particular, the carbon thin film electrode of the present invention has a preferable feature in that an electrode in which gold nanoparticles are uniformly distributed in the electrode can be obtained even when a high concentration of gold nanoparticles is contained.

Moreover, in the carbon thin film electrode containing the gold nanoparticle of the present invention, the gold nanoparticle existing in the vicinity of the surface of the carbon thin film electrode has a structure embedded in the carbon thin film electrode so that a part of the gold nanoparticle is exposed on the surface. It is characterized by. That is, the gold nanoparticles existing near the surface are partially buried in the microcrystalline domain constituting the carbon thin film electrode, and are partially exposed on the electrode surface. The gold nanoparticles arranged in this way are structurally distinguished from an electrode having a gold film attached so as to cover the electrode surface by electrodeposition or the like. The carbon thin film electrode with a structure in which at least a part of the gold nanoparticles are exposed on the surface is highly stable to withstand long-term use while maintaining high sensitivity to arsenic detection. have.
Incidentally, the carbon thin film electrode of the present invention is used for, for example, electrochemical measurement of arsenic by square wave voltammetry, and then the electrode surface is dried with nitrogen gas or the like, and left in the atmosphere at room temperature for a long time. It can withstand repeated use while maintaining high sensitivity. Thus, the gold nanoparticle-containing carbon thin film electrode of the present invention also has long-term storage stability, for example, from the drying treatment after the initial measurement use to the atmosphere at room temperature for 24 hours or more, preferably 120 It exhibits long-term storage stability of more than hours, more preferably more than 240 hours.

The particle size of the gold nanoparticles contained in the carbon thin film electrode of the present invention is preferably 7 nm or less. When the gold nanoparticles are 7 nm or less, a stable embedded structure of the gold nanoparticles on the surface of the carbon thin film is preferable. In particular, from the viewpoint of the above effect, the particle size of the gold nanoparticles is more preferably 5 nm or less, and further preferably 3 nm or less. When the particle size of the gold nanoparticles exceeds 7 nm, the structure in which the gold nanoparticles are stably dispersed and embedded cannot be maintained, and gradually approaches the characteristics of the bulk gold electrode. That is, the signal as an electrode is unstable and noise is increased, which is not preferable.
The particle size of the gold nanoparticles can be observed with a transmission electron microscope, for example, as described in Example 2 below.

  Moreover, it is preferable that the density | concentration of the gold nanoparticle contained in the carbon thin film electrode of this invention exists in the range of 10-22 at%. It is preferable that the concentration of the gold nanoparticles is in the range of 10 to 22 at% because arsenic ions can be detected with high sensitivity and stability. In particular, from the viewpoint of the above effect, the concentration of the gold nanoparticles is more preferably in the range of 15 to 20 at%. When the gold nanoparticle concentration is less than 10 at%, the sensitivity to arsenic ions is low. When the gold nanoparticle concentration is greater than 22 at%, the low noise property derived from the carbon component is lost, and further, the gold electrode As a result, similar measurement stability is lowered, which is not preferable.

Conventionally, when a metal component is contained as a nanoparticle in a carbon thin film electrode by a sputtering method (for example, Japanese Patent Application Laid-Open No. 2003-121407 (Patent Document 5)), the metal component is contained at a concentration exceeding 10 at%. Nanoparticles could not be included in the electrode. However, the concentration of the gold nanoparticles contained in the carbon thin film electrode of the present invention can be controlled by controlling the target power of the carbon target and the gold target, respectively, when the electrode is manufactured by sputtering. It is possible to control the concentration of the gold nanoparticles, and it is possible to control the concentration of the gold nanoparticles within the preferable range. For example, in order to set the concentration of gold nanoparticles in the unbalanced magnetron sputtering method to 10 to 22 at%, for example, the target power of the gold target is adjusted to 80 to 200 W with respect to the power of the carbon target of 400 W. Can be controlled. A person skilled in the art can appropriately adjust each target power arranged independently in the sputtering apparatus so that the concentration of gold nanoparticles is 10 to 22 at%.
The concentration of gold nanoparticles contained in the carbon thin film electrode can be measured by, for example, X-ray electron spectroscopy (XPS method) as described in Example 2 below.

Further, it is desirable that a clear carbon lattice image is observed in the above-mentioned TEM image between the gold nanoparticles, and a microcrystalline domain is also formed. This carbon lattice image is derived from the conductive sp ² bond, and has sufficient conductivity to be used as an electrode. In addition, components derived from sp ³ bonds that have very low electrical conductivity but provide high strength are also introduced into the carbon, thereby providing sufficient chemical strength for use as an electrode.

  In addition, the film thickness of the carbon thin film electrode for electrochemical measurement of the present invention is not particularly limited, but the film thickness of the carbon thin film electrode is about 20 to 200 nm from the viewpoint of securing sufficient conductivity and obtaining desired characteristics. preferable.

  Next, a sputtering apparatus capable of producing the gold nanoparticle-containing carbon thin film electrode of the present invention will be described. A schematic view of a sputtering apparatus capable of producing the gold nanoparticle-containing carbon thin film electrode of the present invention is shown in FIG. In this apparatus, the carbon target 2 and the gold target 3 which are targets are arranged independently, and each target is arranged so as to be sputtered to one point on the substrate 1. As a result, sputtering is performed so that the carbon component or the gold component is concentrated on the rotating substrate 1 from each target, and the gold nanoparticles are uniformly distributed in the thin film formed on the substrate 1. be able to. At that time, it is necessary to form the film while controlling the sputtering power of the carbon target 2 and the gold target 3 independently. Therefore, although it is preferable to control each target power with a separate power supply, it is not limited to such a form.

  The arrangement of the carbon target 2 and the metal target 3 is not limited to the following form, but as shown in FIG. 1 (a), the carbon target 2 is arranged so as to face the plane of the substrate 1, and The metal target 3 can be arranged at an angle so that gold is sputtered onto the substrate 1 at a location away from the carbon target 2. Alternatively, the carbon target 2 and the gold target 3 shown in FIG. As another form, both the carbon target 2 and the gold target 3 can be arranged at an angle with respect to the plane of the substrate 1. Thus, the arrangement location of the carbon target 2 and the gold target 3 is not particularly limited as long as an electrode having desired characteristics can be obtained. The distance between the substrate and the target can be adjusted in the same manner as in the conventional apparatus. At this time, the distance between the substrate and the target is preferably the same between the carbon target 2 and the metal target 3, but may be different. The distance between the carbon target 2 and the metal target 3 and the degree of inclination with respect to the plane of the substrate 1 are not particularly limited as long as an electrode having desired characteristics is produced. With such a configuration of the sputtering apparatus, it is possible to obtain a gold nanoparticle-containing carbon thin film electrode for electrochemical measurement in which the distribution of gold nanoparticles present in the electrode is uniform. In addition, according to the manufacturing method using the sputtering apparatus having such a configuration, the gold nanoparticle content of the gold nanoparticle-containing carbon thin film electrode can be controlled even at a high concentration.

  As described above, the carbon thin film electrode in the present invention can be manufactured by any sputtering method using a sputtering apparatus capable of independently controlling the target power of the carbon target and the gold target. It can be produced by simultaneously depositing a carbon thin film and gold nanoparticles on a substrate selected according to each application by sputtering. As such a formation method, UBM sputtering is preferably used, but magnetron sputtering, RF sputtering, DC sputtering, ECR sputtering, or ion beam sputtering can be used. A person skilled in the art appropriately determines the production conditions of the gold nanoparticle-containing carbon thin film electrode of the present invention in each sputtering method with reference to known documents (for example, JP2003-121407, JP2006-90875, etc.). Can be set.

  Although not limited to the conditions described below, for example, when producing a carbon thin film constituting the gold nanoparticle-containing carbon thin film electrode of the present invention using the UBM sputtering method, a rare gas such as argon gas is used as a sputtering gas. It can be used, and the gas pressure of sputtering gas can be 0.1-10Pa. Sintered carbon (C) can be used for the carbon target, and gold (Au) is used for the gold target. The substrate can be heated at room temperature to 200 ° C., and preferably at room temperature without heating. The target power of the carbon target can be 100 to 500W, and the target power of the gold target can be 10 to 200W. To increase the gold nanoparticle content, the target power of the gold target can be increased relative to the target power of the carbon target. To decrease the gold nanoparticle content, the target power of the gold target can be increased to carbon. What is necessary is just to reduce relatively with respect to the target power of a target.

  As the substrate, for example, a conductive substrate is a silicon single crystal wafer or metal substrate doped with impurities such as boron in a silicon substrate, and an insulating substrate is glass or polydimethylsiloxane (PDMS), Various polymers such as polycarbonate, polyethylene, polypropylene, acrylic resin, polyethylene terephthalate (PET) resin, epoxy resin, and olefin resin can also be used.

  The carbon thin film electrode for electrochemical measurements of the present invention is suitably used when detecting arsenic ions or measuring the concentration of arsenic ions by an electrochemical technique. Examples of an object for detecting arsenic ions by an electrochemical method or measuring the concentration of arsenic ions include water in a natural environment or a working environment, a food-derived aqueous solution, a biological fluid derived from a living body, and the like. However, it is not particularly limited as long as it is a solution containing arsenic ions.

  In such a method, the arsenic ions contained in the measurement target solution that can be detected or measured in concentration are trivalent arsenic ions. However, the use of the carbon thin film electrode for electrochemical measurement of the present invention is not limited to the electrochemical method for measuring trivalent arsenic ions, and is also suitable for the electrochemical method capable of measuring pentavalent arsenic ions. It is possible to use. As an electrochemical method for measuring pentavalent arsenic ions, for example, a method of measuring trivalent arsenic ions by reducing pentavalent arsenic ions to trivalent arsenic ions is known. Thus, the target substance measured by the carbon thin film electrode for electrochemical measurements of the present invention is arsenic (trivalent) or arsenic (pentavalent).

  When arsenic is detected using the carbon thin film electrode for electrochemical measurement of the present invention, arsenic can be measured by an electrochemical measurement method known to those skilled in the art. For example, arsenic can be measured by using the gold nanoparticle-containing carbon thin film electrode of the present invention in the ASV method. When the gold nanoparticle-containing carbon thin film electrode of the present invention is used in the ASV method, those skilled in the art can appropriately set conditions based on known conditions. However, the electrochemical measurement method used to detect arsenic is not limited to the ASV method.

  According to the present invention, there is provided an apparatus for electrochemically measuring the concentration of arsenic ions in a solution to be measured using the gold nanoparticle-containing electrode for electrochemical measurement produced as described above. The apparatus for quantifying arsenic ions of the present invention preferably has an electrochemical cell equipped with an electrode capable of performing ASV measurement of arsenic ions stably and with sensitivity as described above. Further, a measurement kit, a current-potential measurement device, and the like may be combined with members or reagents for constructing the measurement system of the present invention. Further, an on-line measuring device may be obtained by combining a flow cell capable of processing more samples more quickly and a pretreatment device for removing impurities. Furthermore, it is good also as an on-site analyzer by using a micro flow cell etc.

  Moreover, unless otherwise defined, terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms used herein should be interpreted as having a meaning consistent with the meaning in this specification and the related technical field, unless otherwise defined, idealized, or overly formal. It should not be interpreted in a general sense.

  In the following, the present invention will be described in more detail with reference to examples. However, the invention can be implemented in various ways and should not be construed as limited to the embodiments set forth herein.

<Example 1> Production of gold nanoparticle-containing carbon thin film
A gold nanoparticle-containing carbon thin film electrode according to an embodiment of the present invention was formed on a silicon wafer (size: 2 inches) using a UBM sputtering apparatus. Below, the concrete method is demonstrated. As the UBM sputtering apparatus, an apparatus provided with a carbon target and a gold target in the arrangement shown in FIG. 1 (a) was used. Here, argon (Ar) was used as a sputtering gas, and sintered carbon (C) and gold (Au) were used as targets. The gas pressure of the sputtering gas was 0.6 Pa. During the formation of the thin film, the substrate was not heated to room temperature. The target power was adjusted to 400 W for the carbon target and 10 to 200 W for the gold target, and the ion acceleration voltage was 20 V. In addition, the gold nanoparticle content in the carbon thin film electrode was controlled by changing the target power of the gold target during thin film formation.
Under the above conditions, when the target power of the gold target was adjusted to 10 to 200 W, the content of gold nanoparticles in the obtained carbon thin film electrode was 1 to 22 at%.

<Example 2> Characteristics evaluation of gold nanoparticle-containing carbon thin film electrode Next, a gold nanoparticle-containing carbon thin film (film thickness: 40 nm) prepared by adjusting the carbon target to 400 W and the Au target to 160 W, respectively, The particle size of the gold particles, the content of gold nanoparticles, and the bonding state of carbon were observed using a transmission electron microscope (TEM, Hitachi, Ltd.) and X-ray photoelectron spectroscopy (XPS, Shimadzu Corp.). As shown in FIG. 2, from observation by TEM, in the formed gold nanoparticle-containing carbon thin film electrode, gold nanoparticles are dispersed in a carbon microcrystalline domain with a particle size of about 5 nm. Furthermore, the content of gold nanoparticles in the electrode was about 17 at% from XPS measurement. When checking bonding state of carbon by XPS measurement, the ratio of the number of sp ³ bond between atoms to the sum of the number of atoms that are atoms and sp ³ bonds are sp ² bonded was about 0.2.

<Example 3> Electrode characteristic evaluation of gold nanoparticle-containing carbon thin film electrode An insulating tape having a 2 mm diameter hole was pasted on the gold nanoparticle-containing carbon thin film produced in the same manner as described in Example 2. Thus, a carbon thin film electrode having a known electrode area was obtained. This carbon thin film electrode was inserted into a 0.1 mol / L phosphate buffer solution having a pH of 5.0 and connected to a potentiostat (manufactured by CHI Instruments, ALS760). Similarly, the reference electrode (Ag / AgCl) and the counter electrode (Pt) were also inserted into a phosphate buffer solution and connected to a potentiostat.
Next, adjust the concentration of arsenic (trivalent) in the phosphate buffer solution to 1 ppb, 5 ppb, 10 ppb, 20 ppb, 50 ppb, or 100 ppb, respectively. Reduced deposition potential -0.8 V, deposition time 120 seconds, scanning Square wave voltammetry measurement was performed for each concentration at a speed of 1.5 V / sec. The measurement results are shown in FIG. From FIG. 3 (a), the current associated with the oxidation elution of arsenic (trivalent) was clearly observed. From the obtained measurement results, it was confirmed that the oxidation elution current peak increased according to the arsenic (trivalent) concentration. Actually, the relationship between the arsenic (trivalent) concentration and the oxidation current density, as shown in FIG. 3 (b), was found to have high linearity even at a low concentration of 1 to 100 ppb. (Trivalent) was detected.

<Example 4> Electrode stability evaluation of gold nanoparticle-containing carbon thin film electrode Examination of measurement stability with respect to arsenic (trivalent) of a gold nanoparticle-containing carbon thin film electrode produced in the same manner as described in Example 2 did. Using the gold nanoparticle-containing carbon thin film electrode, the measurement was performed with the same configuration as the square wave voltammetry measurement method described in Example 3. The measurement was performed by adding arsenic (trivalent) to the phosphate buffer solution to a concentration of 100 ppb, setting the reduction deposition potential to -0.8 V, the deposition time of 60 seconds, and the scanning speed of 1.5 V / sec. Square wave voltammetry measurements were performed. The result is shown in FIG. In FIG. 4, the solid line is the result of the initial measurement, and the dotted line is the measurement result of the electrode after the initial measurement is finished and the electrode surface is dried with nitrogen gas and left in the atmosphere at room temperature for 24 hours. As is clear from FIG. 4, it was found that the peak current value hardly changed even after 24 hours in the gold nanoparticle-containing carbon thin film electrode, and stable measurement was possible.

  In Example 3 described above, the gold nanoparticle content in the gold nanoparticle-containing carbon thin film electrode was changed, and an arsenic (trivalent) calibration curve was prepared in the same manner as in FIG. The sensitivity increased according to the content of gold nanoparticles present in the. On the other hand, when the stability of the measurement similar to Example 4 described above was evaluated, the stability deteriorated as the content of gold nanoparticles increased. As the content of gold nanoparticles increased, when the carbon component decreased, there was a tendency to show high noise and unstable responsiveness, similar to the characteristics of the gold electrode itself. Therefore, from the viewpoint of highly sensitive and stable detection of arsenic ions, the content of gold nanoparticles in the carbon thin film electrode is preferably about 10 to 22 at%, and more preferably about 15 to 20 at%. I understood.

<Comparative Example 1>
In Example 4 above, an Au electrodeposited GC electrode in which gold was electrodeposited on a glassy carbon (GC) electrode instead of the gold nanoparticle-containing carbon thin film electrode was prepared, and the electrode stability against arsenic (trivalent) under the same conditions It was investigated. The Au electrodeposited GC electrode was inserted into 1 mol / L sulfuric acid containing 0.1 mmol / L tetrachloroauric acid, and the initial potential was 1.055 V, the final potential was -0.045 V, and the scanning speed was 0.075 V / sec. Produced. The measurement results are shown in FIG. Although a peak current (solid line) due to arsenic oxidation was also observed at the electrodeposited Au electrode, the peak current value (dotted line) after 24 hours was about 1/10 compared to the initial measurement result, and the peak current value A significant decrease was observed. Such a result is thought to be due to the loss of activity due to the elution or dropping of gold attached to the surface of the electrodeposited Au electrode.
In other words, by dispersing and containing gold nanoparticles in the UBM sputtered carbon thin film electrode, it is possible for the Au nanoparticles to be present in the carbon very stably compared to the conventional Au-modified carbon thin film electrode. However, it was found that this was a factor that showed a significant advantage in measuring arsenic (trivalent) stably.

  The present invention makes it possible to stably and highly sensitively measure arsenic in a solution by using the gold nanoparticle-containing carbon thin film electrode excellent in reproducibility of production. The electrode has a structure in which gold nanoparticles are embedded in advance so that some of the particles are exposed on the surface, and a conventional electrodeposition process of a gold component on a carbon thin film electrode is required. Therefore, it is possible to provide a measurement method that is simpler and quicker than conventional electrodes. While arsenic is an element harmful to the human body, it is also an industrially important element. Therefore, the present invention is considered to exhibit sufficient power for arsenic environmental monitoring analysis, work environment monitoring analysis, food analysis, geological survey, biological poisoning monitoring, and the like.

Claims (7)

A carbon thin film electrode for electrochemical measurement for detecting arsenic ions in a solution to be measured by electrode reaction based on reduction deposition and oxidation elution,
The carbon thin film electrode for electrochemical measurement is composed of a microcrystalline domain in which sp ² bonds and sp ³ bonds are mixed with respect to the bonding mode between carbons, and thereby a wider range than the graphite carbon electrode and the glassy carbon electrode. Having a potential window, and
A carbon thin film electrode for electrochemical measurement, characterized by containing gold nanoparticles uniformly. The carbon thin film electrode for electrochemical measurement according to claim 1,
A carbon thin film electrode for electrochemical measurement, wherein the content of the gold nanoparticles is 10 to 22 at%. The carbon thin film electrode for electrochemical measurements according to claim 1 or 2,
The carbon thin film electrode for electrochemical measurement, wherein the carbon thin film electrode is composed of a carbon thin film formed on a substrate by independently controlling sputtering power of a carbon target and a gold target in a sputtering method. The carbon thin film electrode for electrochemical measurement according to claim 1,
The atomic ratio of the number of sp ³ bonded atoms to the sum of the number of sp ² bonded atoms and the number of sp ³ bonded atoms between the carbons constituting the carbon thin film electrode is in the range of 0.1 to 0.4. A carbon thin film electrode for electrochemical measurement, characterized in that. The carbon thin film electrode for electrochemical measurements according to claim 1 or 2,
A carbon thin film electrode for electrochemical measurement, wherein the gold nanoparticles have a particle size of 7 nm or less. An apparatus for electrochemically measuring the concentration of arsenic ions in a solution to be measured,
A cell containing a counter electrode and a working electrode comprising the carbon thin film electrode for electrochemical measurement according to any one of claims 1 to 5;
A potential for reducing and depositing arsenic on the surface of the working electrode made of the carbon thin film electrode is supplied by changing a potential of the working electrode made of the carbon thin film electrode in a negative potential direction, and then the working electrode made of the carbon thin film electrode And a potential changing means for supplying a potential for eluting arsenic deposited on the working electrode made of the carbon thin film electrode into the measurement object solution;
An electrochemical measurement apparatus for measuring the concentration of arsenic ions, comprising: a detecting means for detecting a current change accompanying a change in potential of the working electrode made of the carbon thin film electrode. A method for producing a gold thin film-containing carbon thin film electrode for detecting arsenic ions in a solution to be measured by an electrochemical measurement method,
The method includes forming a gold nanoparticle-containing carbon thin film electrode on a substrate by sputtering, and forming a film while independently controlling the target power of the carbon target and the gold target.
Thereby, the gold nanoparticle content in the gold nanoparticle-containing carbon thin film electrode is controlled.

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